Porous organic polymer films are of interest because of their utility as template materials, selective adsorbents, matrices for cell growth in tissue engineering and wound dressings, membranes in separation process, catalytic supports, lightweight structural materials, dielectric materials for electronic devices and optical materials.
It is known that porous particles can be prepared for various purposes, and some porous particles are designed to have marker materials included within discrete pores, which markers allow the use of the particles for specific detection. For example, U.S. Patent Applications 2008/0176157 (Nair et al.) and 2010/0021838 (Putnam et al.) and U.S. Pat. No. 7,754,409 (Nair et al.) describe porous particles and a method for their manufacture, which porous particles are designed to be toner particles for use in electrophotography.
Still another important use of polymeric particles is as a means for marking documents, clothing, or labels as a “security” tag, for example for authentication of documents using an electrophotographic process and core-shell toner particles containing an infrared emitting component and a detection step. For example, U.S. Patent Application Publication 2003/0002029 (Dukler et al.) describes a method for labeling documents for authentication using a toner particle containing two or more mixed compounds having a characteristic detectable signal.
It is also desirable to have an alternative way of marking documents, clothing, or labels with a “security” tag, for authentication of documents using an easier process than use of porous particles containing markers. Product counterfeiting occurs in artworks, CD's, DVD's, computer software recorded on various media, perfumes, designer clothes, handbags, luggage, automobile and airplane parts, securities (for example stock certificates), identification cards (for example, drivers' licenses, passports, visas, and green cards), credit and debit cards, smart cards, and pharmaceuticals. The application of a security marker or taggant to an object or product for authenticating the origin or intended market is known in the art. Security markers can be incorporated into components that make up the object or product, or they can be incorporated into papers, inks, or varnishes that are applied to the object or product, or they can be incorporated into labels affixed to the object, product, or packaging there for. The presence of the security marker can be used to verify the authenticity of the origin of the object using suitable detection means that is specific to the security marker.
Some security markers can be dispersed within a carrier varnish and are referred to as particle-based or pigment-based markers. Such markers remain intact in the varnish and will appear as particles when examined microscopically. Other security markers are dissolvable in an ink or varnish and distributed in the carrier on a molecular level. These markers are not readily detected with a microscope and require more sophisticated detection equipment.
A means for detecting a population of microparticles is described in U.S. Pat. No. 5,450,190 (Schwartz et al.). Groups of microparticles of specific sizes and fluorescent properties or colors are mixed with toner particles and the resulting mixture is used in laser printer cartridges or photocopy machines to provide detectable images.
Particles having two or more different light emitting species can also be printed onto various substrates using various printing means, as described in WO 2007/051035 (Haushalter).
Toner particles having a luminescent material that includes quantum dots are described in EP 2,025,525 (Wosnick et al.) and can be used to form detectable markings on substrates. These toner particles can also include colorants or other detectable components.
Porous particles containing various markers that can be used for specific means of detection are also described in U.S. Pat. No. 8,110,628 (Nair et al.) and U.S. Patent Application Publication 2012/0167666 (Nair et al.) describes porous particles and articles containing same that contain various marker materials within discrete pores for specific means of detection. These porous particles can be prepared using multiple water-in-oil emulsions containing the desired markers and pore stabilizing hydrocolloids to prevent coalescence.
Known methods for the preparation of porous polymer films include the breath figure method to create porous films having uniform pore sizes as described in Science 2001, 292, 79. This method utilizes the condensation of water vapor on the surface of a polymer solution in an organic solvent as droplets that self-assemble at the air-solution interface and, upon evaporation of the solvents, porous polymer structures are obtained. However, this method requires precise control over the processing environment during the fabrication process.
Water-in-oil emulsions where aqueous droplets are dispersed in organic solution of a polymer have been used to make porous films. (J. Phys. Chem. B 2006, 110, 13959-13). Dip-coating the emulsion onto a glass slide and air-drying led to porous polymer thin films. However, such emulsions were only temporarily stabilized and the process was not practical or easily scaled to greater quantities.
U.S. Patent Application Publication 2010/0212928 (Abe et al.) describes the use of water-in-oil emulsions to create organic porous materials as an insulating material around a conductor to provide an insulated wire or cable.
Drug-eluting films loaded with bioactive agents are described in U.S. Patent Application 2012/0027833 (Zilberman). These films are porous and can be prepared by freeze drying a water-in-oil emulsion.
In spite of all the known methods, there still exists a need for a one-step practical, and scalable method for making thin porous organic polymeric films, either as free standing films or films coated onto a substrate for various uses described above. In particular, it would be desirable to have a water-in-oil emulsion that is stable over time that is useful to enable a manufacturable process for creating porous organic polymeric films.
In addition, it would be useful to have porous organic polymeric films that contain various detectably different markers so the films can be used in various security applications.